Scientists Have Genetic Causes Of Autism In Their Sights
Scientists today say they are on track to establish the genetic triggers for autism, paving the way for earlier diagnosis of children who could be at risk of developing the condition and opening up the possibility of inventing new drugs and treatments for the condition.
The identification of a range of rare genetic mutations by an international collaboration known as the Autism Genome Project, involving scientists in the US, Canada and Europe, will further undermine the arguments of those who have claimed that the MMR vaccine, against measles, mumps and rubella, is somehow to blame.
Geri Dawson of Autism Speaks, a charity that helped to fund the research, said that the findings would bring hope to many families who struggle with autism on a daily basis. “What is critical now is to translate these basic biological findings into clinical tools for early detection and treatment.” This would allow children to be helped earlier in life. “We’re now developing behavioural interventions for infants and toddlers who are at risk for autism,” he said.
In the largest study ever into the genetics of autism, the scientists identified rare genetic variations that were 20% more frequent in children with autism than in children without the disorder. These so-called “copy number variations” (CNVs), which can be missing chunks of DNA or extra copies of sequences in and around genes, occur in less than one in 100 people in the general population.
In the study, scientists compared the incidence of these rare CNVs in 996 people with autism spectrum disorders and in 1,287 unaffected people, all with European ancestry. The results, published today in Nature, showed that some of the CNVs were inherited while others were found in children but not in their parents.
Stephen Scherer of the Hospital for Sick Children in Toronto, Canada, said that the research would lead to a paradigm shift in assessing the causes of autism. “Most people in the field believed that autistic individuals shared common genetic variations in just a few genes,” he said. But the research suggests the genetic variations are actually rare. “Most people with autism are probably genetically quite unique, each having their own genetic form of autism. As we discover more of these variants, the number of cases of autism that we can explain increases substantially.”
Identifying the genetic causes means that doctors could develop tests for babies who may be considered at risk of autism based on their family history. “Currently, autism diagnosis is entirely behavioural and lengthy and parents are subjected to a long process where their child is being assessed,” said Louise Gallagher of Trinity College Dublin. “Some children are not getting the diagnosis until as late as five years old. With earlier detection, these children could get earlier interventions, which may limit the severity of the condition.”
Genetic risk is a big issue for families, said Gallagher, as many parents want to know what their risk of having another affected child might be. “With these findings, a proportion of families will be able in the future to get more precise genetic counselling,” she said. “However, it is very early days and we’re not suggesting that pre-natal testing is appropriate because the penetrance of some of these CNVs is incomplete – they may not affect people equally. What we’re saying here is that there’s the potential to identify children at greater risk and to institute earlier intervention.”
Discovery of a major genetic underpinning for autism will help further allay parents’ fears of a sinister environmental cause, such as the link that was proposed by Andrew Wakefield in a paper in the Lancet in 1998. The General Medical Council recently struck him off the medical register over his research ethics. But some parents of autistic children continue to believe he has been the scapegoat for a vaccine scandal, in spite of the absence of scientific evidence for his claims.
The work will also underpin a better understanding of the physiological basis for autism. The risk genes identified in the latest studies are involved in brain functions and knowing what their altered effects are will give scientists targets for therapies. Rare CNVs are also known to play a role in other learning disabilities and in mental health conditions such as epilepsy and schizophrenia.
Anthony Monaco of the University of Oxford, who was part of the consortium, said there was still much more to do to identify the full suite of genetic causes of autism. “This consortium of scientists has been trying to put together a very large jigsaw puzzle without the benefit of having a nice colourful picture on the box. In this paper, the CNVs we found framed this jigsaw puzzle. They give us an idea of what the picture may look like.”